### Designing flyback transformer for capacitor charger 10kVdc, 0.1 µF, 50W

In order to design a flyback C-charger transformer with the Rale Design Software you need the following inputs:

• Min. input voltage and the duty cycle (ton&toff) at this voltage
• DC-output voltages and DC-output currents
• The ripple of the ampere-turns (induction)
• Frequency

There are 2 typical operation modes:

• Continuous mode ts>toff
• Discontinuous mode ts<=toff (typical for C-charging)

The charging & discharging of a capacitor is a dynamic procedure (view the next Figure).

Due to the fact that there is no constant output voltage & current you need to determine by hand (from thermal point of view) the equivalent output voltage and the equivalent output current Note that a flyback transformer is very suitable for charging a capacitor with constant power.

In this operating mode the electronic has to control the constant frequency, the constant ton time and the maximal capacitor output voltage Uc.

During the charging period Tp the capacitor C is empty (Uc = 0 ) and the secondary current will drop down with the formula:  Input Voltage Voltage150V, 1000Hz, ton =100µs, toff = 900 µs Wire Cu, round, single insulated Output Nominal DC output voltage Nominal1470V, max. 10000V Nominal DC output current Nominal 34mA, min. 5mA Wire Cu, round, double insulated, wound outside Core Steel Ferrite N27 Bobbin Type Single section, potted Design Insulation class E, max. operating temperature 120C Criterion of design Temperature rise Ambient temperature 40C

General rules

1. Before you start designing of the flybyck transformer with the above specified input parameters you have to set the Form Factor and the dI/Io:

Form Factor = Tp/2/ton

dI/Io = 100 toff/ts

These 2 input parameters can be calculated if you set q = ton/Tp & s = ts/Tp

or L1 & W1/W2 in the following input mask: 2. Note that discharging time ts varies during the time TL from 900 µs to 71µs.

Due to this fact the operating flyback frequency can not be selected very high.

If the output voltage is over the bobbin testing voltage and the transformer has to be potted then the flyback operating frequency has to be selected less than 2-3kHz.

3. If the commutating losses in the primary leaking inductance are too high then you need to increase ton time.

Design at nominal operation mode 1470V @ 34mA    Design at maximal output voltage 10000V @ 5mA 